--- ray/doc/ray.1	2011/10/27 00:51:29	1.25
+++ ray/doc/ray.1	2023/12/12 20:12:47	1.44
@@ -1,8 +1,8 @@
-.\" RCSid "$Id"
+.\" RCSid "$Id: ray.1,v 1.44 2023/12/12 20:12:47 greg Exp $"
 .\" Print using the -ms macro package
-.DA 10/26/2011
+.DA 11/13/2023
 .LP
-.tl """Copyright \(co 2011 Regents, University of California
+.tl """Copyright \(co 2023 Regents, University of California
 .sp 2
 .TL
 The
@@ -622,6 +622,23 @@ mod trans2 id
 8 red green blue spec urough vrough trans tspec
 .DE
 .LP
+.UL Ashik2
+.PP
+Ashik2 is the anisotropic reflectance model by Ashikhmin & Shirley.
+The string arguments are the same as for plastic2, but the real
+arguments have additional flexibility to specify the specular color.
+Also, rather than roughness, specular power is used, which has no
+physical meaning other than larger numbers are equivalent to a smoother
+surface.
+Unlike other material types, total reflectance is the sum of
+diffuse and specular colors, and should be adjusted accordingly.
+.DS
+mod ashik2 id
+4+ ux uy uz funcfile transform
+0
+8 dred dgrn dblu sred sgrn sblu u-power v-power
+.DE
+.LP
 .UL Dielectric
 .PP
 A dielectric material is transparent, and it refracts light
@@ -932,6 +949,30 @@ invisible from behind.
 Unlike other data-driven material types, the BSDF type is fully
 supported and all parts of the distribution are properly sampled.
 .LP
+.UL aBSDF
+.PP
+The aBSDF material is identical to the BSDF type with two important
+differences.
+First, proxy geometry is not supported, so there is no thickness parameter.
+Second, an aBSDF is assumed to have some specular through component
+(the 'a' stands for "aperture"), which
+is treated specially during the direct calculation and when viewing the
+material.
+Based on the BSDF data, the coefficient of specular transmission is
+determined and used for modifying unscattered shadow and view rays.
+.DS
+mod aBSDF id
+5+ BSDFfile ux uy uz funcfile transform
+0
+0|3|6|9
+     rfdif gfdif bfdif
+     rbdif gbdif bbdif
+     rtdif gtdif btdif
+.DE
+.LP
+If a material has no specular transmitted component, it is much better
+to use the BSDF type with a zero thickness than to use aBSDF.
+.LP
 .UL Antimatter
 .PP
 Antimatter is a material that can "subtract" volumes from other volumes.
@@ -946,8 +987,10 @@ N mod1 mod2 .. modN
 The first modifier will also be used to shade the area leaving the
 antimatter volume and entering the regular volume.
 If mod1 is void, the antimatter volume is completely invisible.
-Antimatter does not work properly with the material type "trans",
-and multiple antimatter surfaces should be disjoint.
+If shading is desired at antimatter surfaces, it is important
+that the related volumes are closed with outward-facing normals.
+Antimatter surfaces should not intersect with other antimatter boundaries,
+and it is unwise to use the same modifier in nested antimatter volumes.
 The viewpoint must be outside all volumes concerned for a correct
 rendering.
 .NH 3
@@ -1151,10 +1194,76 @@ A section of text meant to depict a picture, perhaps u
 font such as hexbit4x1.fnt, calls for uniform spacing.
 Reasonable magnitudes for proportional spacing are
 between 0.1 (for tightly spaced characters) and 0.3 (for wide spacing).
+.LP
+.UL Spectrum
+.PP
+The spectrum primitive is the most basic type for introducing spectral
+color to a material.
+Since materials only provide RGB parameters, spectral patterns
+are the only way to superimpose wavelength-dependent behavior.
+.DS
+mod spectrum id
+0
+0
+5+ nmA nmB s1 s2 .. sN
+.DE
+The first two real arguments indicate the extrema of the
+spectral range in nanometers.
+Subsequent real values correspond to multipliers at each wavelength.
+The nmA wavelength may be greater or less than nmB,
+but they may not be equal, and their ordering matches
+the order of the spectral values.
+A minimum of 3 values must be given, which would act
+more or less the same as a constant RGB multiplier.
+As with RGB values, spectral quantities normally range between 0
+and 1 at each wavelength, or average to 1.0 against a standard
+sensitivity functions such as V(lambda).
+The best results obtain when the spectral range and number
+of samples match rendering options, though resampling will handle
+any differences, zero-filling wavelenths outside the nmA to nmB
+range.
+A warning will be issued if the given wavelength range does not
+adequately cover the visible spectrum.
+.LP
+.UL Specfile
+.PP
+The specfile primitive is equivalent to the spectrum type, but
+the wavelength range and values are contained in a 1-dimensional
+data file.
+This may be a more convenient way to specify a spectral color,
+especially one corresponding to a standard illuminant such as D65
+or a library of measured spectra.
+.DS
+mod specfile id
+1 datafile
+0
+0
+.DE
+As with the spectrum type, rendering wavelengths outside the defined
+range will be zero-filled.
+Unlike the spectrum type, the file may contain non-uniform samples.
+.LP
+.UL Specfunc
+.PP
+The specfunc primitive offers dynamic control over a spectral
+pattern, similar to the colorfunc type.
+.DS
+mod specfunc id
+2+ sval funcfile transform
+0
+2+ nmA nmB A3 ..
+.DE
+Like the spectrum primitive, the wavelength range is specified
+in the first two real arguments, and additional real values are
+set in the evaluation context.
+This function is fed a wavelenth sample
+between nmA and nmB as its only argument,
+and it returns the corresponding spectral intensity.
 .NH 3
 Mixtures
 .PP
 A mixture is a blend of one or more materials or textures and patterns.
+Blended materials should not be light source types or virtual source types.
 The basic types are given below.
 .LP
 .UL Mixfunc
@@ -1551,6 +1660,38 @@ the Ecole Polytechnique Federale de Lausanne (EPFL Uni
 in Lausanne, Switzerland.
 .NH 1
 References
+.LP
+Ward, Gregory J., Bruno Bueno, David Geisler-Moroder, 
+Lars O. Grobe, Jacob C. Jonsson, Eleanor
+S. Lee, Taoning Wang, Helen Rose Wilson,
+``Daylight Simulation Workflows Incorporating
+Measured Bidirectional Scattering Distribution Functions,''
+.I "Energy & Buildings",
+Vol. 259, No. 111890, 2022.
+.LP
+Wang, Taoning, Gregory Ward, Eleanor Lee,
+``Efficient modeling of optically-complex, non-coplanar
+exterior shading: Validation of matrix algebraic methods,''
+.I "Energy & Buildings",
+vol. 174, pp. 464-83, Sept. 2018.
+.LP
+Lee, Eleanor S., David Geisler-Moroder, Gregory Ward,
+``Modeling the direct sun component in buildings using matrix
+algebraic approaches: Methods and validation,''
+.I Solar Energy,
+vol. 160, 15 January 2018, pp 380-395.
+.LP
+Ward, G., M. Kurt & N. Bonneel,
+``Reducing Anisotropic BSDF Measurement to Common Practice,''
+.I Workshop on Material Appearance Modeling,
+2014.
+.LP
+McNeil, A., C.J. Jonsson, D. Appelfeld, G. Ward, E.S. Lee,
+``A validation of a ray-tracing tool used to generate
+bi-directional scattering distribution functions for
+complex fenestration systems,''
+.I "Solar Energy",
+98, 404-14, November 2013.
 .LP
 Ward, G., R. Mistrick, E.S. Lee, A. McNeil, J. Jonsson,
 ``Simulating the Daylight Performance of Complex Fenestration Systems